Radio communication systems, including two-way communication systems are well known in the art. In many such systems, the communication channel (wherein the "channel" may be a dedicated frequency, a frequency or frequency pair allocated pursuant to a frequency division multiplexing scheme, one or more assigned time slots in a time division multiplexed system, a code division multiplexed channel, or other radio frequency communication path) supports transmission and reception of an encrypted signal.
In a typical encrypted system, an original message, such as a voice message, is appropriately processed into an information stream comprising a series of bits. These bits are then further processed pursuant to an encryption scheme to yield an encrypted message.
Typically, any system supporting transmission of digitized information provides for some mechanism to ensure at least an acceptable degree of synchronicity between the reception process and the transmission process, to assure correct decoding of the data. In addition, in an encryption system, an encryption synchronization signal is also additionally provided, which encryption synchronization signal is specifically utilized to assure appropriate decoding of the encrypted message.
In a radio communication system, and particularly a radio system supporting communications in a land mobile environment, communication links are occasionally interrupted for brief intervals due to various interfering phenomena, such as multipath distortion and fading. Upon losing reception of a transmitted encrypted message due to such occasional brief interruptions, a receiver may well lose its previously established encryption synchronization. Consequently, upon subsequently recovering the signal, proper reception and decoding may be unsatisfactory.
One prior art solution to the above suggests interleaving encryption synchronization information from time to time with the encrypted message information, such that the encryption synchronization information is repetitively broadcast. Therefore, if a receiver should momentarily lose reception, synchronization can usually be readily reestablished following the next one (or more) transmission of encryption synchronization information.
The above prior art solution potentially resolves at least some of the problems noted above, but only serves to support continued communications in a relatively simple encryption system. In a communication system that supports use of multiple encryption algorithms and/or encryption keys, reestablishing encryption synchronization alone will often be inadequate to ensure rapid reestablishment of reception and message processing.
Accordingly, a need exists for a radio platform and methodology that will facilitate robust transmission and reception of encrypted messages in an encryption system supporting use of one or more encryption algorithms and/or encryption keys.